Process of preparing casting solutions of ethyl cellulose



Patented Apr. 26, 1949 oNiT-Eo STATES PAIENJ? OFFICE PROCESS OF PREPARING CASTING SOLUL- TIONS OF ETHYL CELLULOSE John H. Prichard; Springfield,.N. Lassignor to I Celanese Corporation of America, a'corporation.

of Delaware No Drawing;- Original application.June.28,.1945,. SerialNo.- 602,165. Divided/and this application August 13, 1948, Serial No. 44,217

5 Claims.

lose or other cellulose others in a volatile solvent medium is Well known. The cellulose ether 'most' commonly employecl commercially is ethyl cellulose which forms tough and'highly'flexible films and foils of excellent stability to light, heat, Water and various chemical agents; The ethyl celluloses employed commercially are available in varying degrees of substitution orethoxyl value, those of a low degree'of" substitution having a 43.5 to 44.5% ethoxyl value; the medium range having a: 44.5 tot'46.8% ethoxyl value and the higher degrees of substitution ranging upwardin'ethoxyl value from 4618 to 50%. Of the ethyl celluloses available; ethyl 'cellulose of an ethoxyl value of 4618? tor 50% is the'm-ost soluble in the usual organic solvents. Ethyl celluloses in the next lower rangeiof substitution, e; g. ethers of 44.5 to 46.8% ethoxylivalue. are quite'hard-an'd tough and possess. a combination of desirable properties-'whi-clt makethem: eminently valuable for use as him or'foil bases. Ethyl celluloses of the latter ethoxyl range are soluble in but re1a-.-

tively few' single solvents and, accordingly, combinations of solvents must be employed. The binary solvent mixture comprising toluene" and ethyl alcohol is quite-"satisfactory for the formation oi'castin'g solutions 1' having a basis of suchethyl cellulose. However, toluene vapors are toxic 2. ingisolution's. Whilesuch mixtures are good'soh ventszf-or ethyl cellu'lose of higher ethoxyl value, e. g: 46;8:.to 49m 50%, at room temperatures; they are not good; solvents for ethyl cellulose of 44.5

to 46.8%. ethoxyl' value. Even at temperatures of 30 to 50 CI, which temperatures are those usually employed during "preparation: and casting ofthe ethyl cellulose solutions, theyproduce onlyswollen'. 01'." gel solutions of ethyl cellulose. Consequently, filmsonfoils have-not been pre aredsatisfactorily when-employing saidsolvent mixtures."

I have nowiound that solvent mixtures comprising. a low molecular weight aliphatic ketone, a low molecular weight aliphatic alcohol having at most 3 carbon atoms and an acetic acid ester of a highermolecular-weight alcohol, namely one containingyat least: 4 carbonatoms may he satisfactorily;employedvforthe preparation of films andwfoils-havingza basis of 'a cellulose ether and especially ethyl' cellulose of :an ethoxyl value of 445x170 46;8%r by solvent castingoperations.

incompletely--soluble in said? solvents, are added toa-solvent'mixture comprising alow molecular weight aliphatic ketone; alcohol and acetic acid ester, and heating; with stirring, the swollen; gel solution underrefluxto' a temperature ofat least 65- (3., andpreferably 65 to 80 C. With temperatures-upto about C., the heating appears to have. substantially no effect upon the solubility characteristicsofthe ethyl cellulose in the ketonev-alcohol-ester solvent mixture. employed. However, when. heating i continued to a temperature of at least C. a sudden and unexpected change in solubility takes place. gelled ethyl cellulose dissolves completely to give a clear, smooth solution. On-cooling to a temperature 5 to 15 C. or even 25. C. below the boiling point of the most volatile solvent com- .ponent and settling, orjust settling without cooling/ps0 as to; eliminate: bubbles, the solution obtained is clear andiree: ofgels and the resulting clear solution may then be employed for casting operations as" wellkn'own in the art. Care musttbe taken not to all-ow the solution to cool excessively so as to cause gelation, which would necessitate; reheating; ofthesolution. The suriaceru-pon which the filmsor foils are cast may In accordance with the novel-processor my inven-' tion, thesevcellulose -ethers, which are normally The be warm, e. g. at a temperature of about 50 C-, or it may be cooler, e. g. at a temperature of 25 to 30 C. When the clear, smooth, heated solution strikes the relatively cool casting surface, a gelation reaction sets in together with the usual solvent evaporation. Films and foils of excellent physical characteristics may be obtained employing the casting solutions prepared by my novel Process.

The fact that the combined eifect of both gelation and evaporation of the heated solution is capable of yielding such excellent films and foils could not be foreseen from any previous knowledge of the film or foil casting art. This is especially so in View of the fact that clear solutions suitable for casting may be obtained by heating above 65 C. then cooling to, say, 50 C. while merely heating to, say, 50 C. does not produce a satisfactory smooth solution capable of being cast. In fact, where the solutions prepared in the latter manner by limited heating are cast, the films or foils so produced are quite unsatisfactory.

The solvent mixtures employed in practicing the novel process of my invention may comprise aliphatic ketones of low molecular weight, such as for example, acetone or ethyl methyl ketone; lower aliphatic alcohol, such as methyl ethyl propyl and isopropyl alcohol; and acetic acid esters of alcohols of higher molecular weight, such as butyl alcohol, isobutyl alcohol, secondarybutyl alcohol, amyl alcohol, isoamyl alcohol and se=condary amyl alcohol.

When forming the ternary solvent mixtures employing acetone as the low molecular weight ketone, the acetone may comprise from 25 to 45% by weight of the solvent mixture, the lower aliphatic alcohol 45 to 65% by weight thereof and the acetic acid ester of the aliphatic alcohol of at least 4 carbon atoms about by weight thereof.

Where ethyl methyl ketone is employed as a component, the solvent mixture may contain 45 to 60% by weight of said ketone, 30 to 45% by weight of the low molecular weight alcohol and about 10% by weight of the acetic acid ester of higher molecular weight aliphatic alcohol. The solution may contain from 20 to 25% by weight of the ethyl cellulose of 44.5 to 46.8% ethoxyl value, the remainder being the solvent mixture.

In some instances it may be advantageous to incorporate certain plasticizers in the casting solutions so as to impart to the ethyl cellulose films and foils greater flexibility or other desirable properties. Suitable plasticizers are, for example,

tricresyl phosphate, dibutyl phthalate, butyl stearate, castor oil or mineral oil and said plasticizers may be present in amounts of from 2 to 25% or more on the weight of the ethyl cellulose in the composition. Suitable resins, waxes, coloring matter and stabilizing agents may also be added, if desired.

In order further to illustrate my invention, but without being limited thereto, the following examples are given:

Example I 25 parts by weight of ethyl cellulose of about 45% ethoxyl value are tumbled at 25 C, with 150 parts by weight of a solvent mixture comprising 60% by weight of ethyl methyl ketone, 30% by weight of denatured ethyl alcoho1 (2B formula) and 10% by weight of butyl acetate. The gelatinous solution obtained is heated to 60 C. with no efiect on the clarity of the solution. At 75 C.

Example II 25 parts by weight of ethyl cellulose of 46.1% ethoxyl value are tumbled at 25 C. with 150 parts by Weight of a solvent mixture comprising by Weight of acetone, 45% by weight of denatured ethyl alcohol (2B formula) and 10% by weight of butyl acetate. No solution takes place at room temperature. The temperature is gradually raised to over C. without any change in solubility being observed. When the temperature reaches C. a sudden change in solubility takes place and a clear solution is obtained. The solution after settling is cast into films while at a temperature of 67 C. The films produced are of excellent strength and clarity.

It is to be understood that the foregoing detailed description is given merely by way of illustration and that many variations may be made therein without departing from the spirit of my invention.

Having described my invention what I desire to secure by Letters Patent is:

1. In a process for the preparation of casting solutions comprising ethyl cellulose dissolved in a volatile solvent medium, the step which comprises adding to a solvent mixture comprising 25 to 60% by weight of a low molecular weight aliphatic ketone, 30 to,65% of an aliphatic alcohol having at most three carbon atoms and about 10% by weight of an acetic acid ester of an alcohol selected from the group consisting of butyl and amyl alcohols, ethyl cellulose of 44.5 to 46.8% ethoxyl value incompletely soluble in said solvent mixture at temperatures up to about 60 C., and raising the temperature of the solvent mixture to 65 to C. whereby said ethyl cellulose is caused to go into solution.

2. In a process for the preparation of casting solutions comprising ethyl cellulose dissolved in a volatile solvent medium, the step which comprises adding to a solvent mixture comprising 25 to 45% by weight of acetone, 45 to 65% by weight of an aliphatic alcohol having at most three carbon atoms and about 10% by weight of an acetic acid ester of an alcohol selected from the group consisting of butyl and amyl alcohols, ethyl cellulose of 44.5 to 46.8% ethoxyl value incompletely soluble in said solvent mixture at temperatures up to about 60 C. and raising the temperature of the solvent mixture to 65 C. to 80 C. whereby said ethyl cellulose is caused to go into solution.

3. In a process for the preparation of casting solutions comprising ethyl cellulose dissolved in a volatile solvent medium, the step which comprises adding to a solvent mixture comprising 45 to 60% by weight of ethyl methyl ketone, 30 to 45% by weight of an aliphatic alcohol having at most three carbon atoms and about 10% by weight of an acetic acid ester of an alcohol selected from the group consisting of butyl and amyl alcohols, ethyl cellulose of 44.5 to 46.8% ethoxyl value incompletely soluble in said solvent mixture at temperatures up to about 60 C., and raising the temperature of the solvent mixture to 65 to 80 C. whereby said ethyl cellulose is caused to go into solution.

4. In a process for the preparation of casting solutions comprising ethyl cellulose dissolved in a volatile solvent medium, the step which comprises adding to a solvent mixture comprisin 60% by weight of ethyl methyl ketone, by weight of ethyl alcohol and 10% by weight of butyl acetate, ethyl cellulose of about 46% ethoxyl value incompletely soluble in said solvent mixture at temperatures up to about C., raising the temperature to 0. whereby said ethyl cellulose is caused to go into solution.

JOHN H. PRICHARD. No references cited. 

